<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="./css/style.css">
    <style>
        .container {
            grid-template-columns: 100px 100px 100px;
            grid-template-rows: 100px 100px 100px;
            grid-template-areas: 'header header header'
                                'main main sidebar'
                                'footer footer footer';
        }
        .item1 {
            grid-area: header;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="item item1">1</div>
        <div class="item">2</div>
        <div class="item">3</div>
        <div class="item">4</div>
        <div class="item">5</div>
        <div class="item">6</div>
        <div class="item">7</div>
        <div class="item">8</div>
        <div class="item">9</div>
    </div>
</body>
</html>